683 
But besides the submarine operations now in action, and which may 
serve to explain most of our ancient phenomena, it has been shown 
that in Russia and other cold countries there are several actual sub- 
aerial processes, by which large blocks are accumulated at different 
heights by the expansion of the ice of rivers, or have been piled up 
by the glacial action cf former lakes, when at much higher levels *, 
leaving lines of coarse angular blocks. » 
I desist, howeyer, in this place from entering further into the many 
features under which the existing agency of ice may be viewed apart 
from the results of the movements of glaciers, More than enough 
has indeed already been said: for so long as the greater number 
of practical geologists of Europe are opposed to the wide extension 
of a terrestrial glacial theory, there can be little risk that such doc- 
trine should take too deep a hold of the mind. But whilst we may 
have no fear of this sort in Kurope, I have lately read with regret 
certain passages in the Anniversary Discourse of Professor Hitch- 
cock of the United States. In North America, striated, scored, and 
polished surfaces of rocks, proceeding from N. to S. for vast di- 
stances, occupy, it appears, at intervals a breadth of 2000 miles, and 
ave seen on hard rocks at all levels from the sea-shore to heights 
of 3000 and 4000 feet. Professor Hitchcock tells us, that these 
phenomena and the accumulations of gravel and blocks had always 
been inexplicable, until the work of Agassiz unexpectedly threw a 
flood of light upon his mind. If Professor Hitchcock could de- 
monstrate what he now seems to believe, that the great mass of the 
continent of North America was formerly covered with ice, he must 
first prove that it was not at that period below the level of the sea ; 
but as yet no facts are before us to lead us to doubt that the great 
accumulation of detritus and the transport of blocks did take place 
beneath the waters in that country. In justice, however, to this 
author, it must be said, that in expounding the glacial theory he 
ingenuously acknowledges the great difficulty of believing that solid 
masses of ice 3000 to 4000 feet thick, covered the whole region; 
that no action of a glacier will explain the persistent striation of the 
surface of an entire continent from N. to S., and that the direction 
of the boulders and the strie is to a great extent up-hill. When 
these and many other difficulties shall have been carefully weighed, 
our transatlantic friends may be disposed to modify their views, par- 
ticularly when they find that the existence of glaciers in Scotland 
and England (I mean in the Alpine sense) are not yet, at all events, 
established to the satisfaction of what I believe to be by far the 
greater number of British geologists. 
* Geological Proceedings, Murchison and De Verneuil on Russia, vol. 
ili. p. 406. 
joAniveNaEiy Address. Philadelphia, April 1841, p. 24. I must be 
excused for stating that Professor Hitchcock has entirely misconceived my 
views, when he places my name among those who had espoused the Alpine 
glacial theory. My efforts have been invariably directed towards its limi- 
tation, nay, to its entire rejection as applicable to by far the largest por- 
tions of the surface of the globe. 
